The present invention relates generally to the field of pulmonology, and more particularly to the field of chronic obstructive pulmonary disease. In this regard, the invention provides devices and methods that are useful in improving breathing in patients with chronic pulmonary disease.
Chronic obstructive pulmonary diseases (COPD) is both very common and increasing in incidence. COPD is the fourth most common cause of death in this country and the morbidity and mortality it causes continue to increase.
COPD comprises chronic bronchitis and emphysema. In both chronic bronchitis and emphysema, airflow obstruction limits the patient""s air flow during exhalation. COPD is a progressive disease characterized by worsening baseline breathing status over a period of many years with sporadic exacerbations often requiring hospitalization.
Typically, patients with COPD have extensive smoking histories; smoking is the major risk factor for development of COPD. Symptoms typically begin in the fifth decade of life with progression to dyspnea on exertion during the sixth and seventh decade. Early symptoms include increasing sputum production, and sporadic acute exacerbations characterized by increased cough, purulent sputum, wheezing, dyspnea, and fever. As the disease progresses, the acute exacerbations become more frequent. Late in the course of the disease, the patient may develop hypercapnea, hypoxemia, erythrocytosis, cor pulmonale with right heart failure, and edema.
Though both chronic bronchitis and emphysema lead to chronic obstruction leading to limitation in expiratory flow, the pathophysiology and clinical presentation of each disease are different. Chronic bronchitis is characterized by chronic cough with sputum production leading to obstructed expiration. Pathologically, there is mucosal and submucosal edema and inflammation and an increase in the number and size of mucus glands. Emphysema is characterized by destruction of the lung parenchyma leading to loss of elastic recoil, reduced tethering of airways, and obstruction to expiration. Pathologically, the distal airspaces are enlarged.
Management of COPD is largely medical and infrequently surgical. Initially, exercise and smoking cessation are encouraged. Medications including bronchodilators (including beta-agonists, anti-cholinergics, and theophylline) and anti-inflammatories are routinely prescribed but are by no means curative. Pulmonary rehabilitation is often prescribed and has been shown to improve quality of life and sense of well being. Long term oxygen is generally reserved for the more severely affected patients. Surgical options are limited and include lung volume reduction surgery and lung transplantation. Both of these surgical options, because of associated morbidity, are infrequently performed.
One of the important components of the aforementioned pulmonary rehabilitation is breathing retraining. This involves teaching the patient new breathing techniques that reduce hyperinflation of the lungs and relieve expiratory airflow obstruction. One of the goals is of course to reduce the level of dyspnea. Typically, these new breathing techniques include diaphragmatic and pursed-lip breathing. This latter technique, pursed-lip breathing, involves inhaling slowly through the nose and exhaling through pursed-lips (as if one were whistling), taking twice as long to exhale as to inhale. Most COPD patients instinctively learn how to perform pursed-lip breathing in order to relieve their dyspnea.
The belief among the medical community is that by producing a proximal obstruction (pursing the lips), the effect is to splint open the distal airways that have lost their tethering. In other words, the affected airways that would normally collapse upon themselves remain open when the patient breathes through pursed-lips.
Medical literature has confirmed the utility of pursed-lip breathing in COPD patients. Specifically, it has been found that respiratory rate is reduced, tidal volumes are increased, and oxygen saturation is improved. All of these contribute to improved dyspnea on the part of the patient. The drawbacks of pursed-lip breathing are twofold. First, because it requires conscious effort, the patient cannot breath through pursed lips while sleeping. As a result, the patient can still become hypoxic at night and may develop pulmonary hypertension and other sequelae as a result. Second, since the patient has to constantly regulate his own breathing, this interferes with his performing other activities.
Clearly, there is a need for a medical device and/or procedure that mimics the effect of pursed-lip breathing without suffering from the above drawbacks. As such, there is much interest in the development of new medical devices and methods for use in procedures for patients with COPD.
According to the present invention, there is a potentially significant benefit for a patient who undergoes a simple procedure that creates an obstruction to expiratory airflow within the airways. There are several possible means of achieving the requisite expiratory obstruction. A device capable of delivering energy (radiofrequency, ultrasound, microwave, laser, cryo) could be used to create a localized scarring or area or stenosis in the appropriate location, most likely in the trachea, main bronchi, or other conducting airways. The goal of this treatment would be to create a proximal obstruction that would alleviate the expiratory limitations caused by the collapse of the smaller distal airways. In COPD, inspiratory airflow is relatively unaffected, so the presence of a fixed obstruction present during both phases of the respiratory cycle would not likely obstruct inspiratory airflow to an appreciable amount.
Another approach would be to implant a device into the airways (most likely the trachea or bronchi) that would create a similar obstruction. This device could either be composed of non-moving parts, or could partially obstruct the airway on expiration and not obstruct the airway on inspiration. That is, the direction of the airflow would determine if the obstruction were present.
Such a device and or methods will mimic the positive benefits of pursed-lip breathing, specifically the increase in tidal volume, decrease in respiratory rate, increase in oxygen saturation, and improvement in patient dyspnea.
In a first aspect, the present invention will provide implantable devices for use in the treatment of COPD. The implantable devices will usually comprise a frame which is implantable within a lung passageway, typically the trachea or a bronchial passage. The frame will include a mechanism or other means for increasing flow resistance to expiration. In a simple embodiment, the flow resistance means will be a simple flow resistor that provides increased resistance to both inspiration and expiration. In such cases, the flow resistor could be a simple plate which is held within the lung passage and which occludes some portion of the luminal cross-sectional area. Preferably, however, the means will comprise a flow resistor which selectively increases resistance to expiration while minimally increasing flow resistance to inspiration. It will be appreciated that the frame could carry a variety of xe2x80x9cone-way valve structures,xe2x80x9d or other flow responsive elements which open to inspiration and close to expiration. Of course, when closing to expiration, the means should not fully occlude the lung passage since the patient must still be able to exhale, albeit at a slower rate in order to assure a more complete evacuation of the lungs.
In a second aspect, the present invention comprises a mouthpiece which a user may conveniently insert and remove depending on need. The mouthpiece will be adapted to fit in the mouth, typically being held between the teeth in the upper and lower jaws. As with the earlier embodiment, the mouthpiece embodiment will increase flow resistance to expiration. Usually, there will be a much lesser increase in resistance to inspiration, although the presence of the mouthpiece will very likely lead to at least a minimal increase in flow resistance to inspiration. In the preferred embodiments, a variety of one-way valves, flaps, or other flow-responsive elements may be provided.
In a third aspect, the present invention provides methods for treating patients suffering from chronic obstructive pulmonary disease (COPD). The methods broadly comprise creating a resistance to expiratory flow in a lung passage, typically the trachea or a bronchial passage. The methods may comprise use of any of the devices desribed above. For example, the flow resistance may be created by implanting a flow resistor, either one with a fixed flow resistance or one with a variable flow resistance, i.e., which is higher to expiration than inspiration. Alternatively, the flow resistance could be increased by modifying a lung passage to decrease the available luminal area. Such methods will typically comprise applying energy to a portion of the luminal wall, typically in the trachea or bronchial passage, so that the lumen decreases in response to the application of energy. In a first specific instance, the energy can be applied in such a way that the wall is injured and scar tissue forms to partially occlude the passage. In a second instance, the energy can be applied under conditions which shrink the collagen in order to close the passage, but where minimal tissue damage and injury response occur.